Woke up to a green pool? Learn how to fix it fast using liquid pool chemicals that work instantly. A practical recovery guide for Australian pool owners.
You walk outside, coffee in hand, and there it is. Your pool has gone from blue to green overnight. It happens to thousands of Australian pool owners every summer, and the good news is it is completely fixable. The even better news? You do not need to drain it.
A green pool is almost always an algae problem, and algae is caused by one thing: not enough active chlorine in the water. Once you understand that, the fix becomes straightforward. This guide will walk you through exactly what to do, step by step, so you can get your pool back to clear, swimmable water as quickly as possible.
Why Your Pool Turned Green
Before you start throwing chemicals at the problem, it helps to understand what actually happened. A green pool means algae has taken hold, and algae needs three things to grow: warmth, sunlight, and low chlorine levels. In Australian conditions, the first two are guaranteed for most of the year, so the only thing standing between you and a green pool is maintaining adequate chlorine.
Here are the most common triggers:
- Chlorine dropped too low. This is the number one cause. It only takes 24 to 48 hours of low chlorine for algae to establish itself, especially in warm weather. A busy weekend of swimming, a hot stretch, or simply forgetting to dose can be enough.
- Your pH drifted too high. When pH rises above 7.6, chlorine becomes significantly less effective. You might have adequate chlorine readings on your test kit, but at high pH levels, very little of it is actually working. Queensland Health’s water quality guidelines recommend maintaining pool pH between 7.2 and 7.6 for effective disinfection. This is one of the most common and most overlooked reasons pools turn green.
- The pump was not running long enough. If your filtration is not circulating the water properly, chemicals cannot reach every part of the pool. Dead spots become breeding grounds for algae, particularly behind ladders, in corners, and along the waterline.
- Heavy rain diluted your water. A decent downpour can dilute chemical levels, introduce phosphates from garden runoff, and drop the pH significantly. After heavy rain in Australia, pools are especially vulnerable.
- The filter needs cleaning. A clogged or inefficient filter cannot remove the fine particles that algae feeds on. If you have not cleaned or backwashed your filter recently, it could be contributing to the problem.
Understanding the cause matters because it tells you what to fix once the pool is clear, so it does not happen again. If you find that the same problems keep coming back, our guide to common pool care mistakes covers the habits that lead to repeat issues.
Step 1: Work Out How Bad It Is
Not all green pools are equal. The shade of green tells you roughly how much work is ahead.
Light green or teal
You can still see the bottom of the pool. The algae bloom is fresh, probably only a day or two old. This is the easiest to fix and often clears within 24 to 48 hours with the right treatment.
Medium green
The water is noticeably cloudy and you can only see about halfway down. The algae is more established. Expect two to three days of treatment and filtration to get back to clear.
Dark green or swamp
You cannot see the bottom at all. The walls feel slimy. This has been building for a while. Recovery is absolutely possible without draining, but it will take three to five days of consistent effort, chemical treatment, and heavy filtration.
Important: Do not swim in a green pool. Algae itself is not the main concern, but the bacteria that thrive alongside it can cause skin irritation, ear infections, and gastrointestinal issues. NSW Health requires pool water to meet specific disinfectant and pH standards before it is safe for swimming. Wait until the water is clear and your chlorine levels have stabilised before getting back in.
Step 2: Get the Chemistry Right First
Before you shock the pool, you need to set the right conditions for the chlorine to actually work. Skipping this step is the single biggest reason people shock their pool and it stays green.
Test your water
Use a reliable test kit or take a sample to your local pool shop. You need to know your pH, free chlorine, total alkalinity, and cyanuric acid (stabiliser) levels. These readings will determine exactly what you need to add and how much. If you are not confident reading your test results, our guide to balancing pool water breaks down each parameter and what it means.
Adjust pH to between 7.0 and 7.4
This is critical. Chlorine is dramatically more effective at lower pH levels. At a pH of 7.2, roughly 65% of your chlorine is in its active form. At a pH of 8.0, that drops to about 25%. So if your pH is sitting high, you could double or triple your shock dose and still not kill the algae.
Use pool acid to bring pH down into the 7.0 to 7.4 range before you shock. If you have ever dreaded adding hydrochloric acid because of the fumes, PoolFlow Zero Fume Pool Acid does the same job without the burning eyes, throat irritation, or corrosion to nearby surfaces. It makes a real difference when you are standing over the pool pouring acid in. You can read more about how it works and why it matters on our blog.
Check your stabiliser (cyanuric acid)
Cyanuric acid protects chlorine from UV degradation, but if levels are too high (above 50 ppm), it also reduces chlorine’s effectiveness. The Australian Standard AS 3633 recommends keeping stabiliser within a range that allows chlorine to remain active. If your stabiliser is very high, say above 80 to 100 ppm, you may need to partially drain and refill before treatment will be effective. No amount of shock will work if your stabiliser is locking up your chlorine.
Step 3: Shock the Pool
Now that your pH is in range and you understand your stabiliser levels, it is time to hit the algae hard with a chlorine shock treatment. The goal is to raise your free chlorine level high enough to overwhelm and kill all the algae in the water.
How much shock to use
The dose depends on how green the pool is. As a general guide for a standard 50,000 litre pool:
- Light green: A standard shock dose (follow product label for your pool size)
- Medium green: Double the standard dose
- Dark green: Triple the standard dose
Why liquid chlorine works better here: When you are shock-treating a green pool, speed matters. Liquid chlorine dissolves instantly on contact with the water, meaning the full dose is working within minutes. Granular shock products need time to dissolve, often leaving undissolved residue sitting on your pool floor, and in some cases they simply do not dissolve evenly. When you are trying to kill an established algae bloom, you want every gram of chlorine in the water and working immediately.
When to shock
Always shock in the evening or at night. UV light from the sun degrades chlorine rapidly, and you want the full dose working through the cool overnight hours when algae is most vulnerable. Add the shock by pouring it evenly around the pool edges while the pump is running.
Step 4: Brush Everything and Run the Filter
This is the step most people skip, and it makes a massive difference.
Brush the walls, floor, and steps
Algae clings to pool surfaces, and brushing physically breaks it loose into the water where the chlorine can reach it. Pay extra attention to corners, behind ladders, around the waterline, and any shaded areas. If the walls feel slimy, brush them thoroughly. You want that algae suspended in the water, not hiding on the walls.
Run the filter continuously
After shocking and brushing, run your pump and filter 24 hours a day until the pool clears. This is non-negotiable. The filter needs to process the entire volume of water multiple times to remove the dead algae. If you only run the pump for your usual 6 to 8 hours, recovery will take significantly longer. CHOICE Australia’s pool maintenance guide also recommends continuous filtration during and after treatment until water clarity is fully restored.
Backwash or clean regularly
As dead algae collects in the filter, flow rate drops and efficiency decreases. For sand or DE filters, backwash when the pressure gauge rises 8 to 10 psi above normal. For cartridge filters, hose them off every 12 to 24 hours during the recovery process. Expect to backwash multiple times over the next few days.
Step 5: What to Expect Over the Next Few Days
Recovery is a process, not an instant fix. Here is a realistic timeline:
Day 1 (morning after shock)
The pool should look different. If it was dark green, it might now be a lighter green or cloudy teal. If it was light green, it may already be cloudy blue or grey. Cloudy is actually a good sign, as it means the algae is dead and now you need to filter it out.
Day 2 to 3
Continue running the filter 24 hours a day. Brush again. Test the chlorine level. If it has dropped back to near zero, the algae consumed it all and you need to shock again with the same dose. Keep the pH in range. Each day the water should look progressively clearer.
Day 3 to 5
For moderate to severe green pools, this is when you should see the water turning from cloudy to clear. If it is still cloudy after three days of filtration, a liquid clarifier can help bind the fine particles so your filter can remove them more efficiently.
The overnight chlorine test
Your pool is truly recovered when it passes the overnight chlorine loss test. Test your free chlorine at sunset, then again the next morning. If you have lost less than 1 ppm overnight, the algae is gone and the water is safe to swim in.
How to Stop It Happening Again
Fixing a green pool once is annoying. Fixing it twice is avoidable. The key is maintaining consistent chlorine levels, because algae cannot grow when there is enough active chlorine in the water. Here is what that looks like in practice:
- Test regularly. Twice a week in summer, once a week in cooler months. It takes two minutes and prevents hours of recovery work.
- Keep pH in check. A pH between 7.2 and 7.6 ensures your chlorine is working at full strength. If you are constantly chasing pH, check your total alkalinity first, as it acts as a buffer that stabilises pH.
- Run the pump long enough. Eight to ten hours a day in summer is the minimum for most Australian pools. Our summer pool care guide covers pump run times and other seasonal essentials in more detail.
- Dose after rain. Heavy rain dilutes your chemicals and introduces contaminants. A quick test and top-up after any significant rainfall prevents the conditions algae needs to get started.
- Use the right products. Liquid pool chemicals dissolve instantly, dose accurately, and leave no residue. When your chemicals are working from the moment they hit the water, there is no gap in protection for algae to exploit. Browse the full PoolFlow range to see what suits your pool.
Get Your Pool Back to Clear, Faster
A green pool is not the disaster it looks like. With the right approach, most pools can go from green to clear within a few days. The difference between a quick recovery and a drawn-out battle usually comes down to three things: getting the pH right before you shock, using enough chlorine, and running the filter hard until the water clears.
PoolFlow liquid pool chemicals are designed for exactly this kind of situation. They dissolve on contact, so every drop is working from the moment it hits the water. No residue, no guesswork, no waiting. Combined with Zero Fume Pool Acid for safe pH correction, you have everything you need for a fast, effective green pool recovery.
Find your nearest PoolFlow stockist and get the products you need to get your pool back.
